1. Field of the Invention
The present invention relates to a magnetic head used for a magnetic tape, one of a magnetic recording medium, in a video tape recorder (VTR), for example, and a method of manufacturing the magnetic head.
2. Description of the Related Art
Along with development in digitalization in recent years, higher recording density is required in a field of magnetic recording. With regard to a magnetic head using a magnetic tape as a recording medium, those excellent in recording/reproducing performance (hereinafter, simply referred to as “head performance”) in its frequency bandwidth to be used are expected. As a magnetic head suitable for realizing such a high recording density, a thin film magnetic head such as a magneto-resistive (MR) head and a bulk-type Metal-In-Gap (MIG) head have been suggested. Among these, in view of reduction in product cost, the bulk-type MIG head is widely employed.
The bulk-type MIG head is formed with, as shown in FIGS. 9A and 9B, a pair of magnetic core halves 21, each comprising a magnetic material, such as ferrite, fitted to abut on each other. A portion where the magnetic core halves 21 abut on each other functions as a magnetic gap 22. A metal magnetic film 23 comprising a ferromagnetic material, such as Sendust, is arranged only in the vicinity of the magnetic gap 22. This arrangement improves the head performance. The magnetic core halves 21 are bonded to each other with low melting glass 24 to be a single body.
For slide contact with a magnetic tape, the MIG head has a slide contact plane 25 formed to be substantially arc. One end of the magnetic gap 22, the metal magnetic thin film 23 arranged in the vicinity of the magnetic gap 22 and the pair of magnetic core halves 21 for sandwiching them is exposed on the slide contact plane 25. In addition, the MIG head has a winding opening 26 positioned substantially at the center of the pair of the magnetic core halves 21 and a coil guide notch 27 provided at an edge of each of the magnetic core halves 21. As illustrated in FIG. 10, a coil wire 28 is wound along a direction substantially parallel to the slide contact plane 25 utilizing the winding opening 26 and the coil guide notches 28.
As described above, the magnetic heads including the MIG head are expected to have excellent head performance. It is considered that improvement of the head performance can be realized by, for example, optimizing the property (such as soft magnetic property), the structure (such as plural laminated films) or the film-forming conditions (such as angle of incidence, direction of easy magnetizable axis) of the metal magnetic thin film 23 for attaining higher permissivity and higher saturation density at the magnetic core in the vicinity of the magnetic gap 22, or by adjusting a crystal direction of the magnetic core halves 21 for reducing noise signals. However, a number of factors affect each other in optimization of the metal magnetic thin film 23 and the crystal direction, a variety of studies are required in a process from development to practical application, that is, it takes quite a long time until the practical application. Accordingly, the above-mentioned ways are not always appropriate from a point of view of earlier practical application and lower production cost.
Alternately, there is another way for solving difficulties in the earlier practical application and the promotion of reduction in production cost that, for example, the number of winding of the coil wire 28 is increased so as to improve the head performance. The more the number of winding of the coil wire 28 increases, the more the recording/reproducing performance of the magnetic head is improved. However, if the number of winding of the coil wire 28 is simply increased, inductance L thereof becomes greater. This may possibly make the value of the inductance L beyond a range of its standard values (rated values).
If a volume of the magnetic core formed with the pair of magnetic core halves 21, that is the volume of the magnetic body, is reduced, increase of the inductance L is suppressed. Thus, it is possible to avoid such a disadvantage described above. However, when the reduction in volume of the magnetic body makes the outside dimension (thickness, width or the like) of the magnetic head smaller, there arise problems that mechanical strength of the magnetism core itself drops, that specification change of a drum on which the magnetic head is mounted is required, and that an area of the slide contact plane necessary for slide contact with the magnetic tape cannot be easily ensured.
In view of the problems as described above, as disclosed in Japanese Patent Application Publication Hei 6-274816, a magnetic head which has a magnetic core with a smaller volume without changing the outer shape of the magnetic head and without deteriorating mechanical strength thereof by forming the magnetic core with a bonded body comprising a magnetic ferrite and a nonmagnetic ferrite laminated thereon. According to the disclosed magnetic head, since it is possible to reduce volume of the magnetic core, increase of the inductance L is suppressed even if the number of winding the coil wire is increased. As a result, it is possible to improve the head performance while solving the problems in mechanical strength and compatibility to the conventional products.
However, in the magnetic head using the magnetic core, since the bonded body in which the nonmagnetic ferrite is laminated on the magnetic ferrite is used, a complicated bonding step in which pressurization at a high temperature (hot press) of 1000° C. or more, for example, is carried out on the magnetic ferrite and the nonmagnetic ferrite is required in addition to usual head forming steps. This makes the productivity largely drop. This may make it unfavorable in promotion of reducing production cost. In addition, since the magnetic core has a two-layer structure comprising the magnetic ferrite and the nonmagnetic ferrite laminated thereon, there is less flexibility in shaping the magnetic core and the magnetic ferrite and the nonmagnetic ferrite cannot be always arranged at appropriate positions. Furthermore, difference in thermal expansion coefficients between the magnetic ferrite and the nonmagnetic ferrite, the bonded body may have distortion or other problems.